Because $this->_class->fieldNames is empty for my class, $columnList will also be empty.
$this->_getSelectJoinColumnsSQL($this->_class) generates
", t1.articleID AS articleID0, t1.relatedArticleID AS relatedArticleID2"
so $this->_selectColumnListSql == ", t1.articleID AS articleID0, t1.relatedArticleID AS relatedArticleID2"